Re: [PATCH] net: ftgmac100: Ensure tx descriptor updates are visible

From: Benjamin Herrenschmidt
Date: Thu Oct 22 2020 - 03:41:41 EST


On Wed, 2020-10-21 at 14:40 +0200, Arnd Bergmann wrote:
> On Wed, Oct 21, 2020 at 12:39 PM Joel Stanley <joel@xxxxxxxxx> wrote:
>
> >
> > diff --git a/drivers/net/ethernet/faraday/ftgmac100.c b/drivers/net/ethernet/faraday/ftgmac100.c
> > index 331d4bdd4a67..15cdfeb135b0 100644
> > --- a/drivers/net/ethernet/faraday/ftgmac100.c
> > +++ b/drivers/net/ethernet/faraday/ftgmac100.c
> > @@ -653,6 +653,11 @@ static bool ftgmac100_tx_complete_packet(struct ftgmac100 *priv)
> > ftgmac100_free_tx_packet(priv, pointer, skb, txdes, ctl_stat);
> > txdes->txdes0 = cpu_to_le32(ctl_stat & priv->txdes0_edotr_mask);
> >
> > + /* Ensure the descriptor config is visible before setting the tx
> > + * pointer.
> > + */
> > + smp_wmb();
> > +
> > priv->tx_clean_pointer = ftgmac100_next_tx_pointer(priv, pointer);
> >
> > return true;
> > @@ -806,6 +811,11 @@ static netdev_tx_t ftgmac100_hard_start_xmit(struct sk_buff *skb,
> > dma_wmb();
> > first->txdes0 = cpu_to_le32(f_ctl_stat);
> >
> > + /* Ensure the descriptor config is visible before setting the tx
> > + * pointer.
> > + */
> > + smp_wmb();
> > +
>
> Shouldn't these be paired with smp_rmb() on the reader side?

(Not near the code right now) I *think* the reader already has them
where it matters but I might have overlooked something when I quickly
checked the other day.

Cheers,
Ben.